[PATCH 1/2] device_cgroup: fix RCU usage

[Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

dev_cgroup->exceptions is protected with devcgroup_mutex for writes
and RCU for reads; however, RCU usage isn't correct.

* dev_exception_clean() doesn't use RCU variant of list_del() and
  kfree().  The function can race with may_access() and may_access()
  may end up dereferencing already freed memory.  Use list_del_rcu()
  and kfree_rcu() instead.

* may_access() may be called only with RCU read locked but doesn't use
  RCU safe traversal over ->exceptions.  Use list_for_each_entry_rcu().

Signed-off-by: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Cc: Aristeu Rozanski <aris-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
Cc: Serge E. Hallyn <serge.hallyn-GeWIH/nMZzLQT0dZR+AlfA@public.gmane.org>
---
Oops, wrong patch.  This is the correct one.

Thanks.

 security/device_cgroup.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -164,8 +164,8 @@ static void dev_exception_clean(struct d
 	struct dev_exception_item *ex, *tmp;
 
 	list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) {
-		list_del(&ex->list);
-		kfree(ex);
+		list_del_rcu(&ex->list);
+		kfree_rcu(ex, rcu);
 	}
 }
 
@@ -298,7 +298,7 @@ static int may_access(struct dev_cgroup
 	struct dev_exception_item *ex;
 	bool match = false;
 
-	list_for_each_entry(ex, &dev_cgroup->exceptions, list) {
+	list_for_each_entry_rcu(ex, &dev_cgroup->exceptions, list) {
 		if ((refex->type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
 			continue;
 		if ((refex->type & DEV_CHAR) && !(ex->type & DEV_CHAR))